I meant: in case of a contract ends (so, work permit and non-B-visa, too) and you fortunately got a new job at another school in the same city...(Sisaket)

Can I get a new 1-year-non-B-visa at the Immigraton Office or do I have to go on a visa run to Laos (Savannakhet) again and again ? Thank you for your reply ....

At the Immigration office you get an extensions of stay, not a visa.

The new regulation allow you to apply with showing you have applied for a new work permit due to changing school.

It is possible to make a smooth transition from one school to another due to recent changes to the rules for getting extensions of stay (not visas).

But you cannot just stop working at one and then get a new job at another school.

Your new school needs to apply for a a work permit for you and obtain an application approval letter from the work permit office.

Then your current school will need to give you a letter stating the date you are no longer working for them. On that date or shortly before you would go to immigration and cancel your current extension then you would apply for a new extension with the work permit application approval letter and documents from the new school.

After your current school or yourself cancels your current work permit the new work permit would be issued.